Instructables
Picture of Welding EMT Conduit
I use EMT (Electrical Metallic Tubing)  conduit in a lot of my projects. EMT is cheap, smaller sizes are bendable and it is readily available at local home supply stores.

There are potential health problems welding EMT however. Please read this (and other Instructables warnings) before you consider welding EMT.

The biggest problem is that toxic fume are given off when the welding arc heats up the galvanized coating on the EMT. These fumes (mostly zinc oxide) are toxic, as in poisonous to breathe!

See this Instructable for a description of the risk: http://www.instructables.com/id/Bicycle-cargo-trailer--200-lb-capacity%2c-%2430-for-pa/step11/Safety-considerations/

NOTE: DO ALL OF THESE STEPS OUTDOORS IN A WELL VENTILATED AREA!

I am an amateur welder (not even close to an expert!) and to minimize the risk as much as possible I use these three steps when welding EMT.

BE CAREFUL. BE EXTRA SAFE. DON'T BREATHE IN ANY FUMES EVER. DON'T GET IN A HURRY AND SKIP ANY SAFETY PRECAUTIONS. USE A RESPIRATOR IF YOU ARE NOT POSITIVE YOU ARE AVOIDING THE FUMES.


 
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Step 1: Vaporize the Coating

Picture of Vaporize the Coating
1. Heat the EMT to vaporize as much of the galvanized coating as possible. I use a MAPP torch (I don't know if propane would work.) to thoroughly heat the area(s) where I will be welding. Do this outside. (Photo #1) The galvanized coating will vaporize and leave a brown residue (Photo #2 arrow)

Step 2: Grind the Surface

Picture of Grind the Surface
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2. Grind the area that you heated. I use a flap-pad in an angle grinder, a wire wheel in an electric drill or an abrasive paint remover for this step. Do this outside. (Photo #1) The result is a bright and shiny steel surface (Photo #2 below the yellow line)

Step 3: Move the Air While Welding

Picture of Move the Air While Welding
3. Weld with a fan (usually on the low setting) gently moving air over and away from the weld zone. Do this outside. (Photo #5) Move the fan around until the air flow moves the fumes away but doesn't blow the shield gas away from the weld arc. This position can change depending on whether it is windy or calm outside.